The Sept. 11 attacks on America 17 years ago this week began the nation’s longest war, a seemingly never-ending battle against terrorists and other enemies of freedom.

But an argument can be made that the horrific attack unleashed another assault on a pillar of democracy: a war on reason, where facts don’t matter and truth is subjective.

There have always been fringe groups espousing conspiracy theories, but the rise of the Internet over the past quarter-century has vastly extended their reach and amplified their impact in a way I didn’t fully comprehend until I became a small cog in what came to be called the 9/11 Truther movement, a small army of doubters who, to this day, wage a disinformation campaign to undercut public confidence in government institutions and the reality-based news media.

My personal experience predates Facebook (2004), YouTube (2005) and Twitter (2006). It centers on a few words taken out of context in a report I gave on CNN as I stood with the burning Pentagon as a backdrop.

“From my close-up inspection, there’s no evidence of a plane having crashed anywhere near the Pentagon,” I said, in answer to a question about whether the American Airlines Boeing 757 may have crashed nearby, short of the building.

The offhand comment was deliberately misrepresented on the Internet as an eyewitness attesting to the fact that no plane hit the Pentagon on Sept. 11, and by early 2002 it had gone viral among conspiracy theorists around the world.

Even now 17 years later that video clip still shows up in my Google alerts, posted to my Facebook page, and just two weeks ago on my Twitter feed, often with the ominous notation. “This footage aired once after 9/11 and was never on TV again!”

Given that the full video clip shows that I was describing what I saw when I went to the crash site, including pieces of the plane “small enough that you can pick up in your hand,” I thought by engaging with the doubters, I could easily correct the record.

But in a decade of lengthy conversations with more than a dozen “truthers,” I never changed a single doubter’s mind.

In 2004, Popular Mechanics decided to examine 9/11 conspiracy theories, and eventually published the book Debunking 9/11 Myths, which marshaled an impressive team of writers, reporters and experts to make the case that such popular myths could not stand up to the facts.

The late Sen. John McCain wrote the forward for the book, in which he argued “any explanation for the tragedy of 9/11 must start and end with the facts,” and praised Popular Mechanics for its “old-fashioned approach” of relying on “reporting, evidence and eyewitnesses.”

“We cannot let these tales go unanswered,” he wrote. “The 9/11 conspiracy movement exploits the public anger and sadness. It shakes Americans’ faith in government at a time when that faith is already at an all-time low.”

As noble an effort as it was, there’s no evidence that meticulous reporting had any measurable effect among the millions (according to opinion polls) who chose to believe an alternate reality.

In fact, shortly after the Popular Mechanics book was published in 2006, another book came out, Debunking 9/11 Debunking, which offered counter arguments for every scientific, fact-based explanation.

The two books now sell side-by-side on Amazon.

What took me a while to grasp is that the reason facts have lost much of their power to change mistaken beliefs is that those false narratives have been weaponized in an ideological war to the point where whether they are true or not is largely irrelevant.

Which brings us to today, and the challenge that responsible journalists have in trying to provide facts and context in a world where the president uses social media to disparage stories he doesn’t like as “fake news.”

Scott Adams, creator of the popular Dilbert cartoon, was one of the first to recognize that candidate Trump’s skills at persuasion would likely carry him into the White House by what Adams describes as ripping a “hole in the fabric of reality.”

Months before the election, Adams wrote extensively about how Trump’s innate ability as a “master persuader” would change the way many Americans feel about reality.

In a March 2016 Washington Post article, Adams is quoted as outlining six principles that he predicted Trump would employ to turn conventional wisdom on its head and vanquish all his rivals.

1. Trump knows people are basically irrational.
2. Knowing that people are irrational, Trump aims to appeal on an emotional level.
3. By running on emotion, facts don’t matter.
4. If facts don’t matter, you can’t really be “wrong.”
5. With fewer facts in play, it’s easier to bend reality.
6. To bend reality, Trump is a master of identity politics — and identity is the strongest persuader.

In his post-election book, Win Bigly, Adams argues that Trump’s real genius is that he grasped something the other candidates didn’t, namely that people don’t use facts and reason to make decisions.

In 2014, I wrote a master’s thesis on the subject of whether facts matter and the persistence of misinformation in the digital age.

But it’s only now — nearly two decades after I became part of a conspiracy theory and failed in my efforts to debunk it — that I truly understand how flawed my worldview is that there is an objective reality that can be understood through rigorous, rational thinking.